The present invention is directed to an assembly for rotating wellbore casing during cementing-in of the casing.
In the cementing-in of casing, the main problem encountered is how to provide a better cement bond between the casing, the wellbore and the cement in the annulus to overcome the problem of water migration between various zones, sometimes termed microchannelling.
Many processes are used in an attempt to enhance cement bonding. For example, cement squeezes, packer zone isolation, and turbolizers are sometimes used. These methods are expensive and complex and are not always effective.
It is common practice to rotate casing in shallow holes (to approx. 1000 m) in order to enhance wellbore cementing. This has been found to noticeably enhance the bond between the casing and the cement thereby decreasing the chance of microchannelling along the casing string. While rotating has been found to be effective at shallower depths, it is not feasible due to the high torque generated to rotate the casing from surface in deeper holes or in bridged-off portions of the hole.
An assembly and method have been invented to provide for rotation of a casing section in a zone of interest without requiring rotation of the casing string from surface. Such rotation enhances cementing procedures. The assembly is particularly useful as it permits rotation in zones of interest such as, for example, in deep sections of the borehole where previously casing rotation was difficult. The assembly is also useful for rotating through bridged-off portions of the hole. The casing section is preferably rotated by passing wellbore fluids such as mud or cement past vanes in the casing section of interest.
Thus in accordance with a broad aspect of the present invention, there is provided: an assembly for connection to a casing string comprising: a casing section connected to the casing string through a bearing device, the bearing device permitting rotation of the casing section relative to the casing string and a means for rotating the casing section relative to the casing string.
The means for rotating the casing section can be a plurality of vanes formed on the casing section and positioned to cause rotation of the casing section by action of well fluids moving therepast. The vanes are preferably formed within the casing section. To provide for removal of the vanes should it be desirable to have access therebelow, the vanes can be formed of easily drillable material such as aluminum or fiberglass.
In accordance with a further aspect of the present invention, there is provided a method for cementing in a casing section at a zone of interest, comprising: providing a casing string with a casing section attached thereto and extending across a zone of interest, the casing section and the casing string each having inner bores and the inner bore of the casing section being in communication with the inner bore of the casing string; and pumping cement through the inner bores of the casing string and the casing section while rotating the casing section at an increased rate of rotation than that of the casing string.
In accordance with another aspect of the present invention, there is provided a method for rotating a section of casing a rate different from any rate of rotation of the casing string to which the section of casing is attached; comprising: providing a casing string and a casing section connected to the casing string through a bearing device, the bearing device permitting rotation of the casing section relative to the casing string and a means for rotating the casing section relative to the casing string; and actuating the means for rotating to drive the casing section to rotate on the bearing device relative to the casing string.